Coffin Bone Loss, Remodeling Associated with Laminitis

Laminitis is a devastating hoof disease in which the interlocking leaflike tissues called laminae anchoring the distal phalanx (DP, or coffin bone) within the hoof become inflamed and fail to support the bone.

Photo: The Horse Staff

High on many equine researchers' wishlists is finding a way to identify signs of impending laminitis sooner, allowing them to begin treatment earlier and hopefully provide a better prognosis for affected horses. Laminitis is a devastating hoof disease in which the interlocking leaflike tissues called laminae anchoring the distal phalanx (DP, or coffin bone) within the hoof become inflamed and fail to support the bone.

Recently, scientists have discovered that osteolysis (dissolving of bone) of the DP is an early sign of laminitis development. To better identify and characterize this process, University of Pennsylvania School of Veterinary Medicine (Penn Vet) researchers evaluated DP disease using micro-computed tomography (microCT). Julie Engiles, VMD, Dipl. ACVP, assistant professor of pathology at Penn Vet's New Bolton Center, presented their results at the 2013 American Association of Equine Practitioners' Convention, held Dec. 7-11 in Nashville, Tenn.

In the study, Engiles and colleagues assessed parasagittal (vertical) bone slices from 36 feet (26 front feet and 10 hind feet), collected in a database established by Hannah Galantino-Homer, VMD, PhD, senior research investigator on laminitis at New Bolton Center, from 15 horses with and without clinical signs or history of laminitis. They evaluated the feet for bone loss using microCT, which can provide detailed information about subtle changes in bone microarchitecture. Engiles said her team's microCT scans provided quantitative measurements indicating bone volume, bone density, and bone mineral density, among others, which they correlated with laminitis severity based on radiographic, gross, and histopathologic changes identified within an adjacent parasagittal slice from each foot.

So how exactly is bone dissolution in the distal phalanx involved with laminitis?

"The inner hoof wall and DP are directly connected via blood vessels that arise within the deep cavities of the bone and extend through bony conduits to supply the overlying soft tissues, including the laminae," Engiles explained. "With chronic laminitis comes dramatic changes to the DP bone architecture that can be seen on an X ray as marginal remodeling and fractures, which were previously attributed to altered biomechanical forces due to laminitis-associated structural changes in the hoof wall. However, in this study, we have identified micro-architectural changes in the bone that occur in the very early stages of the laminitis. These changes reflect an imbalance in bone resorption versus bone formation cycles that can occur from stimuli such as inflammation, alterations in blood flow, or metabolic changes, as well as altered biomechanical forces."

In this study, Engiles said, she and her team determined that DP bone loss did correlate to early and chronic stages of laminitis pathology. She said they observed these bony changes in both performance and nonperformance animals as well as in acute to subacute or mild stages of disease.

"In addition, preliminary microscopic evaluation of the laminitic equine DP shows early activation of medullary spaces (marrow-filled cavities and cellular intervals between the mineralized bone struts) with increases in inflammatory cells, bone demolition, and vascular changes with edema (fluid swelling) that corresponds to the bone loss seen on microCT,” Engiles said. "This supports our hypothesis that the DP is a dynamic structure influenced by many altered states."

Although there is not yet a direct practical application to this early investigative research, Engiles said this study does introduce a novel component of laminitis pathology, highlighting the complexity of both the equine foot's architecture and the disease itself.

"Given the direct anatomic connection between the DP and hoof laminae, the dramatic and early association between laminitis and DP bone pathology, and the potential for activated bone to induce pain, clinicians should consider the potential influence of the distal phalanx on laminitis progression, lameness, or response to therapy," Engiles concluded.

About the Author

Alexandra Beckstett, Managing Editor of The Horse and a native of Houston, Texas, is a lifelong horse owner who has shown successfully on the national hunter/jumper circuit and dabbled in hunter breeding. After graduating from Duke University, she joined Blood-Horse Publications as Assistant Editor of its book division, Eclipse Press, before joining The Horse.

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